With regard to a high-voltage generator, which is one of the elements that constitute an X-ray high-voltage device, included in an X-ray CT apparatus or an X-ray diagnostic apparatus, in order to reduce the size or ensure the dielectric strength voltage, its contents are immersed in insulating oil or is hardened with insulating resin, or the like. Particularly, in X-ray CT apparatuses, as a high-voltage generator is placed on a rotary gantry, all or some of the components, included in the high-voltage generator, are often hardened with resin.
In this case, liquid resin is injected into the container that houses assembled and wired components and is then hardened. The resin injection operation is conducted in a vacuum, or a vacuum defoaming process is performed after resin is injected. This is intended for reduction of spaces, what are called voids, in which resin does not enter, as much as possible. If a void is present in the hardened resin, there is a possibility that the electric field is concentrated (corona discharge) at the void at the time of generation of a high voltage and insulation breakdown occurs. There is a problem in that, if an X-ray CT apparatus, an X-ray diagnostic apparatus, or the like, is used and insulation breakdown occurs in the middle of diagnosis, the apparatus gets damaged and the diagnosis is interrupted.
As secondary winding wires of a high-voltage transformer in a high-voltage generator are wound closely due to a small wire diameter, resin is unlikely to penetrate between the wires. Furthermore, as particulate or fiber-like material, called filler, is mixed to improve the dielectric strength voltage or the radiation performance of resin, it is further difficult to permeate resin between the secondary winding wires of the high-voltage transformer without generating voids.
Furthermore, the relative permittivity of the above-described resin is higher than that of vacuum, air, or insulating oil; therefore, if the secondary winding wires of the high-voltage transformer are hardened with resin, the distributed capacitance between the secondary winding wires is increased. As the wattless current flows into the distributed capacitance between the secondary winding wires, there is a problem in that the wattless current in an inverter circuit, which drives the high-voltage generator, is increased so that the efficiency of the X-ray high-voltage device is lowered and the inverter circuit or the high-voltage transformer gets overheated. Furthermore, as an increase in the distributed capacitance between the secondary winding wires causes a decrease in the resonance frequency of the high-voltage transformer, a rise in the operating frequency of the inverter circuit is constrained, and a reduction in the size of the high-voltage generator is interrupted.